A torque box is a structure with a closed section which can efficiently transmit torsional and bending stresses. Torque boxes are used in a variety of applications, including aerospace and automotive applications. For instance the primary component of an aircraft wing, vertical tail plane and horizontal tail plane is a torque box.
Traditional torque box construction involves a series of processes whereby large components (spars, ribs, covers, stringers, etc) are joined together using mechanical fasteners.
FIG. 1 is a schematic perspective view of a conventional wing box 1. The wing box comprises a front spar 2, a rear spar 3; an upper cover 4 and a lower cover 5, each comprising a stack of fibre-reinforced plies. FIG. 2 shows the front spar 2 and lower cover 5 only. The fibres in the cover 5 are aligned with a cover rosette 6 and the fibres in the spar 3 are aligned with a spar rosette 7 which is generally not parallel with the cover rosette 6.
Each component is optimised for weight by individually tailoring the ply layup for that component. Thus for example a layup for a spar may be 5/7/7/5 (i.e., five 0° plies, seven 45° plies, seven 135° plies, and five 90° plies) while the cover has a layup of the same thickness but more 0° plies (for example 10/6/6/2).